System And Method For Treating Tailings From Bitumen Extraction

ABSTRACT

A system and method for treating tailings from a bitumen froth treatment process such as TSRU tailings. The tailings are dewatered and then combusted to convert kaolin in the tailings into metakaolin. Calcined fines and heavy minerals may be recovered from the combustion products, namely from the flue gas and bottom ash.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/826,166, entitled SYSTEM AND METHOD FOR TREATING TAILINGS FROMBITUMEN EXTRACTION, filed on Jun. 29, 2010, which claims priority fromCanadian Patent Application 2,674,660 filed 17 Aug. 2009 entitled SYSTEMAND METHOD FOR TREATING TAILINGS FROM BITUMENT EXTRACTION, the entiretyof which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to the field of processing ofmined oil sands. More particularly, the present invention relates to thetreatment of tailings from paraffinic froth treatment processes or afroth treatment process that generates tailings comprising hydrocarbons.

BACKGROUND OF THE INVENTION

Oil sands are deposits comprised of bitumen, clay, sand and connatewater, and make up a significant portion of North America'snaturally-occurring petroleum reserves. To produce a marketablehydrocarbon product from the oil sands, the bitumen must be recovered orextracted from the oil sands matrix. Depending on geographic location,bitumen may be recovered by surface mining or in-situ thermal methods,such as steam assisted gravity drainage (SAGD), cyclic steam stimulation(CSS), vapor extraction process (VAPEX), liquid addition to steam forenhancing recovery (LASER) or derivatives thereof

Because the bitumen itself is a tar-like, highly viscous material,separating it from the sands poses certain practical difficulties. Anexample of a common extraction technique is known as a water-basedextraction process, where hot water, air, and process aides are added tocrushed ore at a basic pH to form a slurry. An oil-rich froth “floats”or rises through the slurry as a hydrocarbon phase which can be skimmedoff from the top of a separation vessel. The result is an extract thattypically comprises two parts: a hydrocarbon phase known as a bitumenfroth stream, made up of bitumen, water and fine solids, and an aqueousphase known as extraction tailings, made up of coarse solids, some finesolids, and water. The bitumen froth typically comprises bitumen(approximately 60% by weight), water (approximately 30% by weight), andsolids (approximately 10% by weight), and must undergo a froth treatmentprocess to separate the organic content from the water and solidcontaminants. Due to its high viscosity, the first step is typically theintroduction of a solvent, usually a hydrocarbon solvent such as naphthaor a paraffinic solvent. This step is known as froth separation, andhelps to accelerate the separation of solid particles dispersed withinthe froth by increasing the density differential between the bitumen,water, and solids as well as reducing the viscosity of bitumen.Separation is carried out by any number of methods, such ascentrifugation or gravity separation. Paraffinic froth treatment hasseveral advantages over naphtha-based treatment, as discussed inCanadian Patent Nos. 2,149,737 and 2,217,300. One example of a benefitis the partial rejection of asphaltenes: adding a paraffinic solvent tobitumen froth causes some of the asphaltene component of the bitumenextract to precipitate from the froth and consolidate with the solidcomponents, such as minerals and clays. A further benefit of paraffinicfroth treatment is that, as a result of the adsorption of water dropletsand clays to the hydrophilic sites of the asphaltene molecules, thefinal bitumen product contains only a small amount of emulsifieddroplets and clay particles which can be sources of corrosion andcatalyst poisoning. The details of one method of paraffinic frothtreatment are set out in Canadian Patent No. 2,587,166 to Sury.

The result of the paraffinic froth treatment process is diluted bitumenand a second tailings stream, known as froth treatment tailings, made upof water, solids, and residual hydrocarbon (solvent, rejectedasphaltenes, and un-recovered bitumen) which undergo further treatmentto prepare the tailings for safe disposal. Dilution water is added toavoid foaming within the TSRU (described below) and also the blockage ofassociated tubings and internals The first step in this furthertreatment is to recover solvent through any number of processes knowncollectively as tailings solvent recovery. Recovered solvent may then bereused in the froth separation process. Tailings from a tailings solventrecovery unit (TSRU), known as TSRU tailings, are then disposed of.Table 1 sets out an example of the composition of TSRU tailings:

TABLE 1 TSRU Tailings Composition Component Weight Percent Maltenes 1Asphaltenes 5 Solvent 0 Fines 6.5 Sands 3.3 Water 84.3 TOTAL: 100

The specific properties of the tailings will vary depending on theextraction method used, but tailings streams are essentially spentwater, asphaltenes, unrecovered hydrocarbon, reagents, and waste oreleft over once the usable bitumen has been removed.

While effective, the treatment process requires the use of largequantities of heat, solvent, and water in the form of steam and processwater (dilution water), which significantly increases the costassociated with recovery of petroleum from the bitumen-laden oil sands.

One known method of recovering the water is to simply direct the TSRUtailings into reservoirs known as tailings ponds, and allow the solidcomponents to settle and separate from the water over time. Residualheat escapes into the atmosphere, while the tailings water is retainedfor future use, with some loss due to evaporation. This method is notpreferred for at least three reasons. First, a significant amount oftime is required for most of the solid materials to precipitate out ofthe tailings by operation of gravity alone. Secondly, it does not allowfor the recovery of any of the large amount of energy contained withinthe tailings stream in the form of heat. The heat lost is high, astailings dumped into the ponds are at temperatures between 70° C. and90° C. Thirdly, tailings ponds do not permit recovery of any of theresidual hydrocarbon component within the tailings.

Rather than simply disposing of TSRU tailings, it is desirable torecover a portion of the usable components of the TSRU tailings streamto reduce the overall cost of extracting petroleum resources from oilsands and improve the environmental performance. The energy and waterrecovered can ideally be reused in further steps of the extractionprocess or recycled to the TSRU to be used as dilution water. This hasthe advantage of improving the overall energy efficiency of theextraction process. It is further desirable to minimize the volume oftailings that must be disposed. By removing a certain amount of waterfrom the tailings, the streams can be substantially reduced to mineralsand unrecovered hydrocarbon.

Several attempts to recover heat, water, and other reagents fromtailings streams are known. Methods are disclosed in U.S. Pat. Nos.4,343,691, 4,561,965 and 4,240,897, all to Minkkinen. These patents aredirected to heat and water vapor recovery using ahumidification/dehumidification cycle. U.S. Pat. No. 6,358,403 to Brownet al. describes a vacuum flash process used to recover hydrocarbonsolvents from heated tailings streams. There has been, however, a lackof success in effective water and energy recovery.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at leastone disadvantage of known systems or methods.

In one aspect, the present invention provides a process for treatingtailings from a bitumen froth treatment, such as TSRU tailings, torecover a portion of their water, energy, and residual hydrocarboncomponents. The treatment process requires the minimal use of energy inaddition to the substantial amount of enthalpy already invested in priorstages of the bitumen extraction and froth treatment processes. However,enthalpy can be recovered from both the hot water via dewatering circuitand from the hydrocarbon component of the tailings themselves throughcombustion of the tailings. Thermal energy generated by this process canthen be used in the extraction processes in order to help reduce theexternal energy requirement. This process also assists in the recoveryof other usable materials from the tailings.

In one aspect, the present invention provides a method for treatingtailings containing kaolin and hydrocarbons from a bitumen frothtreatment process, comprising dewatering the tailings and combusting thehydrocarbons in the dewatered tailings stream in a combustion chamber.The combustion chamber is operated at a temperature sufficient to causea chemical reaction converting kaolin into metakaolin. Small particlesof metakaolin may be carried out of the combustion chamber with the fluegas as ‘fly ash’, while particles too large to be suspended in the fluegas may be recovered from the bottom ash. Usable materials such as waterfrom tailings, heat from the combustion chamber, calcined fines, andheavy minerals can be recovered.

In another aspect, there is provided a system for treating tailingscomprising kaolin and hydrocarbons from a bitumen froth treatmentprocess, comprising a dewatering unit for removing water from a tailingsstream and a combustion chamber, such as a circulating fluidized bedboiler, for combusting the dewatered tailings stream, carrying out achemical reaction whereby kaolin converts to metakaolin, and recoveringmetakaolin from either the flue gas or bottom ash streams and. Thesystem may also include elements for recovering usable materials such aswater, heat from the combustion chamber, calcined fines and heavy metaloxides from fly and bottom ashes.

In another aspect, there is provided a method for treating tailings froma bitumen extraction or froth treatment process, the tailings comprisingsand, clay comprising kaolin, and water, and hydrocarbons, the methodcomprising: dewatering the tailings to produce a dewatered tailingsstream and a water stream; combusting the hydrocarbons in the dewateredtailings stream in a combustion chamber to cause a chemical reactionconverting kaolin into metakaolin and to produce a flue gas and a bottomash, the flue gas comprising metakaolin. The bottom ash may be used forsolidifying or stabilizing bitumen extraction tailings. Alternatively,calcined fines may be separated from the bottom ash stream and used forsolidifying or stabilizing bitumen extraction tailings, or as anadditive to cement. Alternatively, metakaolin may be separated from thecalcined fines and used for solidifying or stabilizing bitumenextraction tailings, or as an additive to cement. The fly ash, calcinedfines recovered from the fly ash, or metakaolin separated from thecalcined fines, may be used for solidifying or stabilizing bitumenextraction tailings, or as an additive to cement. The bitumen extractiontailings may comprise mature fine tailings, thickened tailings, amiddling stream, naphthenic froth treatment tailings froth flotationtailings, or coarse tailings.

In another aspect, there is provided a system for treating tailings froma bitumen froth treatment process, the tailings comprising sand, claycomprising kaolin and water, and hydrocarbons, the system comprising: adewatering unit for removing water from a tailings stream, producing adewatered tailings stream and a tailings water stream, and a combustionchamber for combusting the dewatered tailings stream, carrying out achemical reaction whereby kaolin converts to metakaolin, and producing aflue gas and a bottom ash stream, wherein the flue gas comprisesmetakaolin.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 is a flow diagram illustrating an overview of a method oftailings treatment according to one disclosed embodiment;

FIG. 2 is a schematic of an example of a tailings treatment system inaccordance with one disclosed embodiment;

FIG. 3 is a schematic of an example of a dewatering process using athickener unit in accordance with one disclosed embodiment;

FIG. 4 is a schematic of an example of a dewatering process using ahydrocyclone and thickener unit in accordance with one disclosedembodiment;

FIG. 5 is a schematic of another example of a dewatering process using ahydrocyclone and a thickener unit in accordance with one disclosedembodiment;

FIG. 6 is a schematic of another example of a dewatering process using ahydrocyclone and a thickener unit in accordance with one disclosedembodiment;

FIG. 7 is a schematic of an example of a dewatering process using twohydrocyclones in accordance with one disclosed embodiment;

FIG. 8 is a schematic of an example of a process for separatingcombusted materials in accordance with one disclosed embodiment; and

FIG. 9 is another example of a process for separating combustedmaterials in accordance with one disclosed embodiment.

DETAILED DESCRIPTION

Generally, in one embodiment, the present invention provides a methodand system for treating TSRU tailings using combustion to recover usablesolid components and steam. The following description sets out severalembodiments of the present invention using the example of tailingsproduced from paraffinic froth treatment processes. However, theembodiments discussed herein are also applicable to other treatmentprocesses for bitumen froth or another industrial application thatresults in combustible, kaolinite-bearing tailings.

FIG. 1 shows a high-level outline of the steps involved in the tailingstreatment process in accordance with one embodiment of the invention.Once froth separation tailings undergo tailings solvent recoveryprocessing such as discussed above, they form a stream of TSRU tailings100 comprising water, solid materials, unrecovered hydrocarbons, andunrecovered solvent. Dilution water is added to avoid foaming withinTSRU and also the blockage of associated tubings and internals. Inaddition, the TSRU tailings contain a significant amount of heat energy,as they may be released from a TSRU at a temperature of approximately70° C.-93° C., or about 90° C. Owing to the high specific heat capacityof water, much of the heat energy of the tailings is stored within thewater portion of the tailings. As such, both the water and a significantportion of the enthalpy lost to TSRU tailings can be extracted from thetailings stream and used in, for example, other steps in the oil sandsextraction process. Accordingly, one embodiment of the inventionprovides for a dewatering step 110 where recovered hot water 120 isextracted from the stream. The resulting dewatered tailings 130 isreduced in both volume and water content, so further treatment of theseresulting dewatered tailings 130 may require less heat energy.

As noted above, TSRU tailings contain a substantial amount ofhydrocarbon (i.e. asphaltenes, unrecovered bitumen and solvent). Inaccordance with one embodiment of the invention, these hydrocarbons canbe used as a source of energy. Examples of dewatering methods aredescribed below with reference to FIGS. 3 to 7. Further, using thesehydrocarbons may mitigate the environmental challenge of tailings fordisposal, since the amount of solvents and asphaltenes released into theenvironment can be significantly reduced. Accordingly, in one embodimentof the invention, dewatered tailings 130 undergo combustion 140 usingthe hydrocarbons as a fuel following dewatering 110. Combustion 140 maybe more efficient as a result of dewatering 110, as dewatered tailings130 will combust more readily owing to the removal of recovered hotwater 120. Ammonia, urea, and limestone may be added to the combustionfor emission control.

As noted above, a constituent element of the solid portion of TSRUtailings is kaolinite, or solids rich in kaolin. Kaolin, which has achemical formula of Al₂Si₂O₅(OH)₄, undergoes dehydration at temperaturesof approximately 500-1000° C. to form metakaolin according to thefollowing chemical reaction:

2Al₂Si₂O₅(OH)₄→2Al₂Si₂O₇+4H₂O

Accordingly, during combustion 140, the kaolin content of dewateredtailings 130 will undergo the above dehydration synthesis to formmetakaolin once the temperature during combustion is high enough toreach the activation energy threshold for the reaction. Combustion 140results in two product streams: flue gas 150 and bottom ash 160.

In one embodiment, the metakaolin product of the reaction will form as afine solid, and exit combustion 140 as part of flue gas 150. Heavierparticles will settle and be removed with the bottom ash. Separation 180is then used to extract calcined fines 190, including metakaolin, whichhas several industrial applications owing to their cementitious, orpozzolanic, properties. The emission 195 is also shown. Metakaolin is awell-known supplement for Portland cement; in addition, it is known toincrease the comprehensive and flexural strengths of cement, andimproves the resistance of concrete against corrosive chemicals andfreeze-thaw conditions. Similarly, metakaolin may be used as a mainingredient of a geopolymer for stabilizing and solidifying wastestreams. Accordingly, the calcined fines extracted from flue gas 150 andbottom ash may be used to treat other tailings streams, such as maturefine tailings (MFT), coarse tailings, or another suitable tailingsstreams resulting from the various stages of oil sands extractionprocesses. The remaining components of flue gas 150 are then released asemission 195, for example CO, CO₂, SO_(x), NO_(R), and H₂O, or arefurther treated.

Bottom ash 160 comprises the coarse tailings remnants from combustion140, which may include sand, clays (including larger sizedmeta-kaolinite particles), minerals, heavy metal oxides, gypsum, andunreacted limestone. Heavy minerals are defined herein as mineralshaving a specific gravity greater than about 2.85, and including,without being limited to, such minerals as rutile, ilmenite, leucoxene,siderite, anatase, pyrite, zircon, tourmaline, garnet, magnetite,manzite, kyanite, staurolite, mica, and chlorite Among these, rutile andzircon are considered valuable materials; for example, zircon isparticularly valued for its applications as an abrasive and an insulatoras well as its refractory properties, while rutile is used in thepreparation of pigments and refractory ceramics. One embodiment of theinvention provides for heavy minerals recovery 170 to extract a portionof the valuable constituents of bottom ash 160. Examples of methods toremove heavy minerals 175 include gravity, magnetic, and electrostaticseparation. Coarse tail 176 comprises the remaining minerals and clayportions left over following heavy minerals recovery 170, and may thenbe disposed of, used for tailings stabilization, or used for furtherseparation of gypsum and unreacted limestone.

FIG. 2 shows a system in accordance with one embodiment of theinvention. TSRU tailings 200 from bitumen paraffinic froth treatmentprocesses enter dewatering unit 210, where a portion of, or much of, thewater in the tailings stream is separated. The dewatering unit may be asole dewatering unit or may comprise at least two dewatering units.Non-limiting examples of suitable dewatering operations methods using ahydrocyclone, centrifuge, filters, settling vessels, or thickeners, allwith or without the addition of chemical aids; however, another processcapable of removing water from a TSRU tailings stream may functionwithin this embodiment of the invention. As a result of the dewatering,TSRU tailings 200 have been split into tailings water 205 and dewateredtailings 215. Tailings water 205 then optionally enters fines removalunit 220 to recover fine particulate matter that may not have beenremoved by dewatering unit 210. Examples of fines removal units includefilters, centrifuges, thickeners, and cyclones.

Examples of dewatering methods are described further below withreference to FIGS. 3 to 7. Recovered hot water 206 may then be used inany number of suitable applications. As noted above, TSRU tailings maybe released from the TSRU at temperatures of approximately 90° C., sorecovered hot water 206 may leave fines removal unit 220 with enthalpythat may be used in, for example, another step of the oil sandsextraction and/or treatment processes that require heat energy. Further,the water itself may be reused in other extraction or treatment stepsincluding, but not limited to, further froth treatments. The recoveredwater may be recycled to the TSRU to be used as dilution water. Anyfines 207 recovered by fines removal unit 220 may then be added todewatered tailings 215 and undergo additional treatment along with therest of the solid components from dewatering unit 210.

Dewatered tailings 215 then enter combustion chamber 230. Optionally andpreferably, combustion chamber 230 is a fluidized bed combustionchamber. Broadly speaking, fluidized beds are solid materials, usuallyparticulate, that are subjected to certain conditions to cause them toexhibit the properties and behaviors of a fluid. In the fluidized bedcombustion in accordance with this embodiment of the invention, solidfuels (shown as chamber bed 231) are suspended on an upwardly-blowingcurrent of air 234, causing a tumbling action that mixes gas and solid.In one embodiment of the invention, chamber bed 231 is at leastpartially made up of particulate matter from the dewatered tailingsthemselves. The fluidized bed combustion should be operated at atemperature so as to form the metakaolin. Limestone, ammonia and ureamay be added for emission control.

Dewatered tailings 215 contains hydrocarbon molecules such asasphaltenes rejected during paraffinic froth treatment, unrecoveredbitumen and residual solvent that may not have been recovered by theTSRU. When ignited, these hydrocarbon components will combust within thechamber, releasing heat energy. As one of ordinary skill in the art willappreciate, fluidized bed combustion allows for effective reactions andtransfer of heat. The presence of non-combustible solid material incombustion chamber 230 may not adversely affect the combustion process,and the presence of some water within the boiler feed (i.e. 215), whichin this case is dewatered tailings 215, may reduce the combustiontemperature in the chamber depending on the technology employed. Incombustion processes, the presence of a certain amount of watermoderates the flame or the bed temperature. Advantageously, this mayreduce the amount of NO_(x) formed during the combustion since a lowercombustion temperature reduces the NOx generated from the combustionair. In one embodiment, combustion chamber 230 is a modified circulatingfluid bed combustion boiler where the bed 231 comprises sand and fines.

According to another embodiment of the invention, heat generated duringthe combustion operation may be recovered. Water 232 is introduced to,for example, a series of pipes or a compartment within combustionchamber 230 so that it is in thermal contact with the interior of thecombustion chamber. As the combustion proceeds, generated heat energyflows into water 232. As a result of heat transfer water 232 willconvert to steam 233 and exit combustion chamber 230. Steam 233 may beat any pressure and temperature desired for use as to drive a steamturbine, as a heat and/or water source for any other step of the oilsands extraction or treatment processes or any other industrial processthat may require it.

In some cases, there may be a high sulfur content in the tailings,particularly in the asphaltene components. As such, a SO_(x) removalstep may be considered for the design of any combustion process used inaccordance with one embodiment of the invention. In a non-limitingexample where combustion chamber 230 is a fluidized bed boiler, theintroduction of limestone in the fluid bed may be effective for theSO_(x) removal. In one embodiment of the invention, the presence of acaustic within the TSRU tailings stream can mitigate a SO_(x) problem,as it is known that caustic reacts with SO_(N). Caustic is a goodabsorber of acidic gases like SO₂ that will naturally form in thecombustion process as the hydrocarbon in the tailings contains sulphur.Moreover, the solid content of TSRU tailings contains materials withsimilar molecular structures of natural zeolites; they may help toreduce SO_(x) emissions during the process.

The combustion proceeds, burning the tailings and converting them to twostreams: flue gas 235 and bottom ash 240. As discussed above, the kaolinclay component in the tailings will undergo dehydration synthesis toform metakaolin when the temperature inside the combustion chamberreaches the 500-1000° C. threshold. In one embodiment, fine tailingssourced from any stage of the oil sands extraction process (i.e. MFT,middlings, or flotation tailings) that produces kaolin-containing finetailings 229 may be introduced into combustion chamber 230. In thismanner, additional tailings can be added, thus increasing the kaolincontent of the tailings in combustion chamber 230 and, consequently, theproduction of metakaolin by dehydration synthesis. Moreover, anyresidual hydrocarbon in the fine tailings will be combusted, recoveringuseful heat from an otherwise waste product. The produced metakaolin aswell as other calcined fines, such as Illite and smectite that will emitfrom the combustion chamber as a portion of flue gas 235 or bottom ash240.

It should be noted that the temperature in combustion chamber 230 mayexceed 1000° C. during combustion. This may have a negative impact onthe pozzolanic properties of the calcined fines; accordingly, oneembodiment of the invention provides for a optimal design for thecombustion for example, by using a staged combustion, primary,secondary, tertiary air addition, proper temperature distribution withinthe chamber can be achieved and the length of exposure of the calcinedfines to high temperatures can be reduced, thus mitigating any damage tothe fines. The addition of water, inert or near inert products (such asmature fine tailings (MFT) with a low hydrocarbon content) may also beadmitted in various locations to assist in temperature control. In oneembodiment, calcined fines contained within flue gas 235 are separatedby flue gas separator unit 250 to form calcined fines 252. Non-limitingexamples of appropriate separation devices include a cyclone and a baghouse filter.

Following separation, flue gas 235 is reduced to solid-free flue gas251, which may be made up of the gaseous components released duringcombustion. In a further embodiment, heat energy contained in flue 251may be reused in other stages of the oil sands extraction/refinementprocesses. For example, flue 251 may be used to dry other tailingsstreams such as MFT using a spray dryer. A spray dryer is a type ofdryer in which the materials to be dried are sprayed to the dryer andthe water is removed by contacting with hot air or hot gas. In thiscase, hot gas can be flue gas. As noted above, bottom ash 240 comprisessand, gypsum, unreacted lime, and metakaolin. and may contain valuableheavy minerals. In one embodiment, bottom ash 240 are introduced intoheavy minerals recovery unit 260 where they are subjected to recoveryoperations to retrieve as much usable and valuable components from thetailings as possible. Non-limiting examples of heavy minerals recoveryunit 260 include devices typically used for electrostatic or magneticseparation techniques, although another suitable method for extractingheavy minerals from a coarse or fine particulate solid or coke may beused in additional embodiments of the invention. The resulting productsfrom heavy minerals recovery unit 260 include heavy minerals 262 andcoarse tail 261, which is mainly made up of sand, calcined fines,gypsum, unreacted limestone and impurities. Coarse tail 261 may then bedisposed of or used in any appropriate manner.

FIGS. 3 to 9 show examples of dewatering and fines removal to preparethe feed for the combustion process described herein. FIG. 3 outlines adewatering method where a flocculent 302 and a coagulant 304 are addedto tailings 306 and this mixture is added to a thickener unit 308 inwhich the recovered water (explained below) 310 is sprayed 312. Thedewatered tailings 314 are then sent to a combustion unit. Hot water 316is removed from the thickener unit 308 and a portion of the hot water316 is recycled for use as spray water 310 and is mixed with theflocculent 302, coagulant 304, and tailings 306.

FIG. 4 outlines a dewatering process in which a hydrocyclone isadditionally used. This method is similar to the dewatering method ofFIG. 3 and includes the following like elements and streams: flocculent402, coagulant 404, tailings 406, thickener unit 408, spray water 410,spraying 412, stream to be combusted 414, and hot water 416. However,tailings 406 are fed to a hydrocyclone 418 to separate fine particlesplus water, indicated as stream 420, which is then fed into thethickener unit 408, with course residue stream 422 which is combinedwith the fine residue 424 exiting the thickener unit 408 to form stream414 to be combusted.

FIG. 5 outlines an alternative dewatering step where the flocculent 502and coagulant 504 are added to tailings 506 prior to feeding thetailings into hydrocyclone 518. The fine particles and water 520 exitthe hydrocyclone 518 and are fed into the thickener unit 508. Courseresidue 522 also exit the hydrocyclone 518 and is combined with fineresidue stream 524 to form stream 514 for combustion. The hot water 516is also shown exiting the thickener unit 508. Spray water 510 andspraying 512 are also shown.

FIG. 6 outlines another dewatering step using a hydrocyclone and athickener. As in previous figures, flocculent 602, coagulant 604,tailings 606, fine particles and water 620, course residue 622, fineresidue 624, stream to be combusted 614, hot water 616, spray water 610,spraying 612, and hydrocyclone 618 are shown. In this process,additional flocculent 626 and additional coagulant 628 are fed to thewater recycled into stream 620. As seen in FIGS. 5 and 6, flocculantsand coagulants may be added at a single point or at multiple locations.

FIG. 7 outlines a dewatering process using two hydrocyclones. Tailings706 are fed into hydrocyclone 718 from which fine particles and water720 are removed and combined with flocculent 702 and coagulant 704,which mixture is then added to the second hydrocylone 730. Hot water 716is extracted from the second hydrocyclone 730. Course residue stream 722is also extracted from the first hydrocyclone 718, and is combined withfine residue stream 724 to form stream 714 for combustion.

FIG. 8 outlines the separation of combusted materials. The dewateredtailings 800 are shown entering the combustion chamber 802. Limestone,urea, ammonia and fine tails 804 may also be added. Flue gas 806 is fedto a flue gas separation unit 808 from which cleaned flue gas 810 flowsalong with fly ash 812. The fly ash 812 is fed to a separation process814 along with bottom ash 816 exiting the combustion chamber 802. In theseparation process 814, some of the materials that may be separatedinclude heavy minerals and metakaolin (collectively 818) and sand,gypsum, unreacted limestone, and impurities (collectively stream 820).

FIG. 9 is another example outlining the separation of combustedmaterials. Elements 900, 902, 904, 906, 908, 910, 912, 914, 916, 918,and 920 are like elements or streams with corresponding numbers in FIG.8. However, in FIG. 9, a distinct separation process 920 is used toseparate elements such as heavy minerals and metakaolin (collectively922) and sand, gypsum, unreacted limestone, and impurities (collectively924) from the fly ash stream 912. Separation process 914 is used toseparate such materials from the bottom ash 916.

Several other advantages of treating tailings streams through combustionin accordance with embodiments of the present invention may include, butare not limited to: recovering of hot water from TSRU tailings,eliminating or mitigating the need to purchase gas or other fuels forextraction, producing steam for extraction and mining processes,eliminating or reducing the volatile organic compound content ofemissions from tailings, producing usable metakaolinite throughdehydration synthesis of the kaolinite content of TSRU tailings,recovering heavy minerals and/or heavy metal oxides from TSRU tailings,reducing the need to store toxic streams in tailings ponds, and reducingthe volume of tailings ponds.

The calcined fines comprising metakaolin and/or the metakaolin producedin the bottom ash may be used to solidify or stabilize a fine tailingsstream (e.g. mature fine tailings (MFT)) resulting from bitumenextraction, or as an additive to cement. When added to cement,metakaolin may mitigate an alkaline condition and may provide a greaterheat resistance. As an example of how metakaolin can be used as anadditive to cement, Advanced Cement Technologies, LLC (Blaine, Wash.,USA) markets PowerPozz™, a high reactivity metakaolin. According totheir data sheet, the product has been successfully incorporated intoapplications for concrete and related products including highperformance, high strength, and light weight concrete; precast andrepetitive products; fiberglass products, ferrocement, and glass fiberreinforced concrete; dry bagged products such as mortors, stuccos,repair material, and pool plaster; and specialty uses such as blendedcements, oil well cementing, shotcrete, decorative interior concretefixtures, and sculture.

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments of the invention. However, it will be apparent to oneskilled in the art that these specific details are not required in orderto practice the invention.

The above-described embodiments of the invention are intended to beexamples only. Alterations, modifications and variations can be effectedto the particular embodiments by those of skill in the art withoutdeparting from the scope of the invention, which is defined solely bythe claims appended hereto.

1. A system for treating tailings from a bitumen froth treatmentprocess, the tailings comprising sand, clay comprising kaolin, andwater, and hydrocarbons, the system comprising: a dewatering unit forremoving water from a tailings stream, producing a dewatered tailingsstream and a tailings water stream; a combustion chamber for combustingthe dewatered tailings stream, carrying out a chemical reaction wherebykaolin converts to metakaolin, and producing a fly ash and a bottom ash;and a calcined fines fly ash recovery unit for recovering calcined finescomprising metakaolin from the fly ash or a calcined fines bottom ashrecovery unit for recovering calcined fines comprising metakaolin fromthe bottom ash.
 2. The system of claim 1 wherein the dewatering unitcomprises at least two dewatering units.
 3. The system of claim 2wherein the dewatering unit comprises a hydrocycloning unit for removingcoarse residue and a thickening unit for removing fine residue.
 4. Thesystem of claim 3 wherein the thickening unit uses a flocculent, acoagulant, and dilution water to flocculate fine particles for removal.5. The system of claim 4 wherein the flocculent and the coagulant areadded to the thickening unit at a single injection point.
 6. The systemof claim 4 wherein the flocculent and the coagulant are added to thethickening unit at multiple injection points.
 7. The system of claim 4wherein the dilution water is a portion of hot water separated from thethickening unit.
 8. The system of claim 7 wherein a portion of the hotwater separated from the thickening unit is for spraying at a waterinterface in the thickening unit to assist in settling of lightasphaltene aggregates.
 9. The system of claim 4 wherein the flocculentused in the thickening unit is anionic polyacrylamide.
 10. The system ofclaim 1 wherein the bitumen froth treatment process is a paraffinicfroth treatment process.
 11. The system of claim 1 wherein the tailingsare tailings solvent recovery unit tailings.
 12. The system of claim 1wherein the combustion chamber is for converting kaolin to metakaolin at500° C. to 1000° C.
 13. The system of claim 1 comprising the calcinedfines fly ash recovery unit.
 14. The system of claim 1 comprising thecalcined fines bottom ash recovery unit.
 15. The system of claim 1wherein the combustion chamber is a fluidized bed combustion chamber.16. The system of claim 15 wherein the fluidized bed combustion chambercomprises a bed, the bed further comprising material from the dewateredtailings stream, and inert products derived from bitumen mining.
 17. Thesystem of claim 16 wherein levels of calcium, and alkalinity in thetailings liquid are consumed to react with SO_(x).